In recent years, downsizing and sophistication of audio visual devices, i.e., so-called AV equipment, are rapidly progressing. Downsizing and sophistication are particularly remarkable in cellular phones, smartphones, tablet PC (personal computer) terminals, and the like. However, since downsizing and sophistication are simultaneously progressing, devices mounted on each equipment are desired to be smaller and thinner. Speaker devices mounted on each equipment are no exception, and are desired to be smaller and thinner like other devices. However, downsizing of a speaker device causes degradation of reproduction performance, particularly, reproduction frequency band or reproduction efficiency, and therefore, conventional techniques have limitations in downsizing and reproduction performance.
As a conventional art, there is a speaker device in which a magnetic fluid is disposed in a magnetic circuit to improve reproduction performance of the speaker device (refer to Patent Literature 1, for example). FIG. 14 shows the conventional speaker device disclosed in Patent Literature 1).
In the speaker device shown in FIG. 14, a voice coil 106 is disposed in a magnetic circuit composed of a plate 101, a magnet 102, and a yoke 103, and a diaphragm 104 is vibrated. A magnetic fluid 107 is disposed between an outer peripheral portion of the plate 101 and an inner peripheral portion of the voice coil 106 to separate a space at a front surface of the diaphragm 104 from a space at a rear surface of the diaphragm 104. Thus, a sound emitted from the front surface of the diaphragm 104 and a sound emitted from the rear surface of the diaphragm 104 are prevented from canceling out each other, and rolling vibration of the diaphragm 104 is prevented, and further, Joule heat generated in the voice coil 106 is caused to escape to the magnetic circuit. In addition, the diaphragm 104 is supported by a plurality of edge pieces 105 in combination with the magnetic fluid 107. Thus, as compared to a case where the entire outer periphery of the diaphragm 104 is supported by a single edge, the compliance of the supporting system supporting the diaphragm 104 is increased, thereby realizing reproduction of a low frequency band in spite of a small diameter.